Generally, a cooperative relaying scheme is a communication scheme of transmitting a signal using a plurality of paths generated by at least two communication nodes having an equivalent function, relaying the signal to a destination via at least one path, combining or selecting the signal received from the plurality of paths, and inferring transmission information.
An existing cooperative relaying scheme may be embodied as various types, and the cooperative relaying scheme having been researched until now may be generally classified into a simple relaying scheme, a cooperative transmission diversity scheme, or a cooperative receiving diversity scheme.
The simple relaying scheme (Institute of Electrical and Electronics Engineers (IEEE) 802.16j Baseline Document, IEEE 802.16j-06/026r4) may divide an entire cell into a plurality of small coverage areas using a plurality of relay stations. In this instance, all relay nodes may reuse the same wireless resource, thereby increasing an additional system volume, however, a service outage rate increases due to high-efficient modulation based on a Carrier to Interference and Noise Ratio (CINR) and interference between cells due to frequency reuse. As described above, the simple relaying scheme has a limit due to service outage in a relay station coverage boundary despite a throughput increase effect using the relay station.
The cooperative transmission diversity scheme (IEEE 802.16j Baseline Document, IEEE 802.16j-06/026r4) is a scheme of acquiring a diversity gain since either a base station or a relay station performs space-time coding. In this instance, the space-time coding uses Alamouti coding, and is respectively classified into full encoding and half encoding based on whether the coding is performed by the base station or is performed by the relay station. Generally, a cellular system uses a Decode-and-Forward scheme by which the relay station performs modulation and demodulation and transmits a signal to the mobile station. Transmission must be simultaneously performed in two nodes in order to perform a conventional cooperative transmission diversity scheme. In the conventional cooperative transmission diversity scheme, when the cooperative receiving diversity scheme is performed using two relay stations, the signal must be transmitted from the two relay stations to the mobile station, and resources must be respectively allocated to the two relay stations. As described above, since the conventional cooperative transmission diversity scheme abandons a portion of resources allocated for the mobile station for which the relay station provides a service in order to secure two diversity paths, band efficiency decreases due to additional resource allocation despite performance enhancement due to the cooperative receiving diversity scheme.
The cooperative receiving diversity scheme (J. N. Laneman, D. N. C Tse and G. W. Wornell, Cooperative Diversity in Wireless Networks: Efficient Protocols and Outage Behavior, IEEE Trans. Inform. Theory, Vol. 50, No. 12, December 2004) does not require additional resources for securing a diversity path since the mobile station overhears the signal when the base station transmits the signal to the relay station. However, since a conventional cooperative receiving diversity scheme requires an additional process for reporting in advance when and via which area resource the signal is transmitted by the base station so that the mobile station may overhear the signal transmitted from the base station, the band efficiency decreases as the additional resources are consumed for performing the additional process.
Accordingly, a selection standard of adaptively selecting a cooperative relaying scheme by reflecting an advantage and a disadvantage of the conventional simple relaying scheme, the cooperative transmission diversity scheme, and the cooperative receiving diversity scheme needs to be disclosed.